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Computer's Heat May Unmask Anonymized PCs
Posted by
Zonk
on Sat Dec 30, 2006 01:49 AM
from the i-seee-you dept.
from the i-seee-you dept.
Virtual_Raider writes "Wired is carrying a story about a method developed by security researchers to identify computers hiding behind anonymity services. From the article: 'His victim is the Onion Router, or "Tor" — a sophisticated privacy system that lets users surf the web anonymously. Tor encrypts a user's traffic, and bounces it through multiple servers, so the final destination doesn't know where it came from. Murdoch set up a Tor network at Cambridge to test his technique, which works like this: If an attacker wants to learn the IP address of a hidden server on the Tor network, he'll suddenly request something difficult or intensive from that server. The added load will cause it to warm up.'"
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Hot enough to... (Score:2, Funny)
FTA: Clock Skew, not temp. (Score:5, Informative)
Of course, the defense to this attack is probably something along the lines of:
$ man nice
Re:FTA: Clock Skew, not temp. (Score:5, Informative)
The idea of using some sort of timing attack against such a network is interesting. There are probably better methods, though.
One idea that springs to mind is that such P2P systems use caches. If you could generate enough requests to flood the cache system, you can force any computer to query nearby computers, where the latency will be roughly equal to the number of hops along the critical path. It then becomes similar to the game of "Black Box", where you try to map particles by throwing rays in and seeing what happens. If you have a sufficiently large latency map from a sufficiently large number of entrance points, you should be able to derive the whole of the exposed topology of the P2P network and be able to identify which of those servers carry what data.
(Think about it. Those of us in Open Source have all done reverse engineering, we have all tried to wrest the secrets of some black box we can't see the inside of, and eventually we have all succeeded in doing so. Our interpretation may not 100% match the internals literally, but they WILL 100% match the internals logically. And in the end, that's all that matters.)
Parent
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The computers I tested it with were normal desktop machines. They all had fans, and in some cases were thermostatically controlled. The differences in temperature were only 1–2 C, but that could be remotely detected.
An oven-controlled crystal might be accurate enough (<1pp
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One idea that springs to mind is that such P2P systems use caches. If you could generate enough requests to flood the cache system, you can force any computer to query nearby computers, where the latency will be roughly equal to the number of hops along the critical path. It then becomes similar to the game of "Black Box", where you try to map particles by throwing rays in and seeing what happens. If you have a sufficiently large latency map from a sufficiently large number of entrance points, you should be able to derive the whole of the exposed topology of the P2P network and be able to identify which of those servers carry what data.
Nice idea, but it wouldn't work on Tor. The topology of the router network depends on who is using it, as routing paths are decided by the machines using the Tor network to remain anonymous, not by the routers themselves. In the case of a hidden service on Tor, a directory server is used to associate a .onion TLD with several routing paths the clients can use to contact to the server. Little information can be derived from the routing paths themselves, as the address of each router in the sequence is encr
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In many ways I agree, but literal != logical. If I spoof the behaviour you look for, I could 'frame' another server for my processes. Log
Randomize the clock (Score:5, Insightful)
Since this and other such attacks are based on analyzing very small changes in the target system clock, even a tiny amount of randomization or pseudo randomization would be effective.
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For most hidden services, either should be feasible. Timing doesn't seem that important anyway, given the inherent latency of the Tor network.
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Even if the clock oscillator were part of the CPU package, adding some random variation to the CPU cooler fan speed would defeat this.
Re:Randomize the clock (Score:5, Insightful)
Parent
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Not necessarily.
If you have your CPU-intensive app running at a low priority, and TOR running at a higher priority, then your CPU will become slightly hotter when TOR is doing heavy processing.
It may make it much harder to detect than it already is, but there you go.
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Why would heavy processing by TOR make the CPU run hotter than heavy processing by $SOME_APP ? It's still just heavy processing, CPU at 100% usage.
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WHA!?! (Score:2)
Great heat source (Score:2)
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utterly useless? (Score:4, Interesting)
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Hidden services are something different than a Tor user. A hidden server is reachable via some hostname in the
Easy solution... (Score:2)
Curiously (Score:2)
Hold on (Score:2)
Far simpler method... (Score:2)
2. DDoS a server, not enough to kill it but slow it down a lot
3. Measure response times to hidden service
4. If all requests using different paths now are slow, you got it
Also, that attack scales to detect multiple hidden sites simultaniously - hit one server, request ten sites and see who answers quickly and not. It's just a consequence of depending on one machine. The only way you could totally avoid that is to not have services at all, only distributed datastore like e.g. Freenet.
Simple Defense (Score:5, Insightful)
Since date and time information isn't included in TCP/IP packets, this kind of attack won't work for all services. Assuming that the "hidden servers" in question are HTTP servers, there is a rather simple workaround: simply disable sending the "Date" header. This can probably be accomplished with mod_headers [apache.org] in Apache, but I've never tried using it myself. Oddly enough, the server would still be standards compliant [w3.org]. Obviously, servers that leak the current time by some other means would still be vulnerable.
A simpler, less precise attack of this nature would simply be to continuously ping the suspected server via both Tor and the public internet. If they (reproducibly) fail at the same time (and we could launch a denial-of-service attack to make it fail), they're probably the same machine. Attacks of this nature might even be able to confirm if a hidden server is on the same network as another computer.... But any of these attacks require someone to suspect you of running the server in the first place—and if they do, you probably have bigger problems to worry about.
The bottom line is, as Tor's manual clearly indicates [eff.org], having a hidden server machine accessible from both Tor and the internet is a bad thing. Operators of hidden services should use a dedicated machine and block all incoming traffic (on all TCP and UDP ports) that is not via Tor.
The answer is RC5, or SETI (Score:2)
Time Sync Early And Often (Score:2)
What if there were a time sync server in the setup whose whole purpose in life is to keep track of the time?
Have no other apps running on it, so that it has negligible system load. All the other systems in the TOR could be set up to sync their time with it every few seconds, i.e. before clock drift becomes detectable. Might check each and every second so as to intentionally cause a collision on the time server and add some randomness. Or, do a time sync every random(1..10) seconds. Or, use multiple NIC
Use NTP to defend against all clock skew attacks (Score:5, Interesting)
The correct defense is the same as the last time:
a) Make sure that there is no system clock skew, by running Network Time Protocol (NTP) on all servers.
b) Make sure that all externally visible timestamps are based on the system clock.
Part (b) is the only difficult step, since many current IP stacks use a private counter/clock instead of the system clock, presumably to reduce the overhead of providing timestamps. I know that Linus T have discussed using user-level library code to provide microsecond resolution (or better) timestamps, with very low overhead:
The library code can just query the cpu/system timer, multiply by the current scale factor (which depends on things like dynamically variable cpu clock frequency), and add the base time which was stored by the OS on the last HW clock interrupt: Total runtime, including call/return overhead can be below 100 clock cycles, which is fast enough to use it everywhere timestamps are needed:
BTW, I wrote asm code to do exactly this inside Novell's NetWare OS a little over 10 years ago. In NetWare these timestamps were used by the Packet Burst algorithms which optimized packet transmission rates.
Terje
Re:I didn't RTFA, but... (Score:5, Informative)
See what reading the article gets you? A tiny nugget of useless information.
Parent
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Fix it with NTP? (Score:5, Interesting)
Parent
Re:Fix it with NTP? (Score:5, Insightful)
One must remember TOR doesn't guarantee strong anonymity, for that you need something like Herbivore [cornell.edu].
Parent
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Re:I didn't RTFA, but... (Score:5, Informative)
Parent
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According to TFA, no. Now maybe you want to R it.
Re:I didn't RTFA, but... (Score:5, Funny)
Parent
Re:I didn't RTFA, but... (Score:5, Funny)
consider your id: 223197
then, consider the fact that you found "You must be new here" a novel response - at least novel enough for you to use it. let me just say, *You* must be new here.
P.S. i hope the recursive irony - including my ID and the parent posters ID - is self evident. no need for recursive "*You* must be new here" replies. please think of the children.
P.P.S. i don't really think recursion is the right word. but the fact that an 'older' user is declared 'new' by a newer user on each child post should lead to a division by zero, a black hole, or at least a bazzarro world somewhere... or it might just be my bed time.
Parent
Re:I didn't RTFA, but... (Score:4, Funny)
Everyone knows that no number of P.P.P.P.P.P.P.S.s that you can add will prevent SOMEONE from posting this very comment.
Parent
Re:I didn't RTFA, but... (Score:5, Funny)
Parent
Re:I didn't RTFA, but... (Score:4, Funny)
awww
Parent
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STFU, noob.
Waiting, waiting, waiting.....
Re:I didn't RTFA, but... (Score:5, Insightful)
His software lets you pinpoint servers in the anon TOR network, good trick, but ultimately useless (since its the users computer you are trying to find).
Of course the other problem is "giving it a heavy load" define heavy load? is it just a little more than usual? or does it mean you have to heat board (he goes off system clock, maintained by a frequency crystal on the MB), most data centres I would think would be fairly efficient at routing even high heat loads out of enclosures and away from the machine.
And then, whoever he does this to can sue him for DoSing their machine, if they can prove (and its not overly difficult) that heat damages computer parts, he can be nabbed for wilful destruction of property as well, since his whole exercise heats the machine for no other reason than locating it.
Then of course, the only way to "heat up" said computer is to do it through the TOR api, which i am guessing most anon servers are built to handle very well (since that would be their primary task).
Oh, and this of course neglects to take into account that your TOR requests may be handled by many many servers in a cluster, each one heating and skewing at different rates...
Ok, its late on a Saturday afternoon and I can poke that many holes in his trick (even if only one is at all real), gimme a good 2-3 hours with some energy drinks in me and I can find more I am sure ^_^
If he can prove it works (and successfully do something usefull with it) in the real world, then it would be a better story.
Parent
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And here I thought he was executed via hanging. Instead...
Death by Boonga-Boonga!!!
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In most cases, the wouldn't even need to be near your house. A well-positioned amp-meter with remote sensing could tell you if the CPU suddenly needed more power.
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Somehow I don't think that would meet the standard for evidence...
You need to measure tiny variations in current caused by one device, mixed in with the haystack of all the other electric devices in your house... Most of which can vary significantly from moment to moment.